1. Field of the Invention
The present invention relates generally to an electron beam deflection yoke provided with electromagnets or coils for deflecting electron beams generated in a cathode ray tube, and more specifically to magnetic field correcting permanent magnets arranged within a ferrite core for an-inline color cathode ray tube.
2. Description of the Prior Art
In a color cathode ray tube used with a color television picture device, there have conventionally been known various methods of incorporating permanent magnets in a deflection yoke in order to correct magnetic field, that is, beam misconvergence or raster distortion. In deflection of electron beams within a cathode ray tube, the deflection effect upon the electron beams depends upon a resultant magnetic field of a magnetic field generated by horizontal and vertical deflecting coils wound around a magnetic deflection yoke and a magnetic field generated by the above-mentioned magnetic field correcting magnet. Therefore, in the case where permanent magnets are used for correcting the magnetic field which may causes the raster distortion, beam spot distrotion or beam misconvergence, the permanent magnets are usually disposed within the deflection yoke in an appropriate space formed between the horizontal deflecting coil and the vertical deflecting coil, for instance. As an example, Japanese Published Unexamined Patent Application No. 57-121136 discloses a method of fixing magnetic field correcting magnets within the deflection yoke, in which the magnet plate is magnetized so that a pair of North and South poles are formed at both the ends thereof along the longitudinal direction thereof as designated by numeral 10 in FIG. 1.
By the way, in the case where the magnets 10 are fixed within the deflecting yoke, it is indispensable to prepare within the deflecting yoke a space in which the magnets are disposed, and further it is peferable to prepare the space as small as possible, because the space will exert a harmful influence upon the deflection efficiency of the horizontal and vertical deflecting coils.
In the prior-art magnetic field correcting permanent magnet, however, since the magnets are magnetized as explained with reference to FIG. 1, when the thickness of the magnet 10 is reduced to decrease the space within the magnetic yoke, the magnetic field generated by the magnets is inevitably weakened, thus resulting in a problem in that it is impossible to sufficiently correct the beam misconvergence or the raster distortion.